let drivers provide map address to pan_kmod_bo_mmap
The intended use case will be to implement vkMapMemory2 https://github.com/KhronosGroup/Vulkan-Docs/pull/1906.
VK_EXT_map_memory_placed lets the user replace the mapping with mapping
of a VkDeviceMemory at the desired
address. To implement that, we'll pass the address the user wants to map
their memory at and a MAP_FIXED
flag.
Edited by Caterina Shablia